This application studies the mechanisms accounting for inflammation and fibrosis in the model of tubulointerstitial disease following obstruction of the urinary tract. The principal investigator hypothesizes that within hours of ureteral obstruction there is increased expression of the renin angiotensin system within the renal cortical proximal tubules. The increased epithelial production of angiotensin II stimulates the angiotensin II type I receptor and this increases the proximal tubule production of osteopontin. This is a potent chemoattractant for macrophages and this leads to the infiltration of macrophages and such macrophage-dependent mechanisms of inflammation and injury as is dependent on TGFbeta1. There are three specific aims: The first specific aim will investigate the critical role of increased osteopontin expression after urinary tract obstruction via its capacity to attract macrophages to increase cortical TGFbeta1 expression. This specific aim will utilize an osteopontin knockout mouse in which the effects of obstruction in this knockout model will be examined from the standpoint of evolution of interstitial disease assessed histologically, and by immunohistochemistry and by in situ hybridization. These studies would be complemented by in vitro studies in which primary cultures of proximal tubular suspensions from osteopontin knockout and wild-type mice will be studied for their ability to induce attraction of macrophages. The second specific aim is to determine proximal tubular angiotensinogen, angiotensin-converting enzyme, and angiotensin II type 1 receptor mRNA and protein, and ACE activity during the initial as well as during the sequential time points for up to 168 hours post-ligation. The third specific aim will mechanistically determine the roles for ACE and angiotensin II type 1 receptor activation in the expression and macrophage attraction, effects of osteopontin using an in vivo rat model of experimental hydronephrosis, and an osteopontin knockout mouse model. In these studies the renin angiotensin system will be manipulated with the use of an ACE inhibitor, enalapril, and an AT-1 blocker, losartan.